As a solid state light source, LEDs (light-emitting diodes) emerged in the sixties of the 20th century and are a product with long life span, firm structure, low power consumption and flexible dimension such that they are becoming to take the place of conventional high pressure halide lamps in a wide range of lighting applications. However, LEDs would generate comparatively high heat energy, with a result of their high light fades and shortened life span. This leads to limited applications of LEDs to some extent.
A currently available LED lamp, which is used for the purpose of illumination, usually comprises a plurality of LED light sources with a lampshade to reach the required illuminance and power, because a single one LED light source has relatively low illuminance and power. The greater the number of the LED light sources is, the more luminous and efficacious the LED lamp is. FIG. 1 illustrates a LED lamp available in the prior art. The LED lamp of FIG. 1 has a plurality of LED light sources 1 mounted equally and horizontally on a same panel 2, wherein each of the LED light sources is arranged on a same horizontal plane with a lampshade and then assembled with a common lamp holder 3 to form a common PAR lamp found in the market. As shown in FIG. 2, this PAR lamp may satisfy the requirement for illuminance, but it does not have specialized means for heat conduction and heat dissipation. As a consequence, the heat energy generated by the plurality of LED light sources cannot be effectively dissipated, such that the temperature of the housing of the lamp is so high to the extent that people would get scalded and that this lamp is vulnerable to get burned out. Moreover, because of the absence of light-condensing elements, the light emitting from the LED light sources cannot be condensed effectively, with the result of light loss and low light availability.
Chinese Utility Model No. 200820101329.7 with the title “LED Light Fixture” discloses a LED road lamp which has a plurality of light units each consisting of a LED light source and a light cover mounted on a horizontal panel relative to a centrally vertical axis of the housing of the lamp, wherein each of the LED light sources is arranged on a same horizontal plane. The lamp of this Chinese utility model made an improvement in thermal dissipation, but it is designed such that all the LED light sources are facing outward. Therefore, most of the luminous flux emitting from the LEDs directly project onto a supposed working surface to generate glare and dazzle and affect people's eyes. Also, this lamp is unable to condense the light and its light efficacy is affected. Because all of the LEDs are arranged horizontally on the same plane, the lamp is definitely large in size if it is made to have a higher power.
According to the LED lamps in the prior art, there is about 90% to 100% of their luminous flux that project onto supposed working surfaces, which leads to the problems of thermal dissipation and short life span. The projection angles of these LED lamps are fixed and cannot be adjusted or changed according to the needs in the practice, which inevitably results in limited applications of these LED lamps. As mentioned above, the output of lights is dazzling and can do harm to people's eyes if the eyes come in direct contact with the lights. Moreover, there is no condensation of lights emitting from these LED lamps, and so their luminous efficiency are comparatively low.
Therefore, there is a need for improving the currently available LED lamps used for the purpose of illumination in terms of their thermal dissipation and light condensation. If the thermal dissipation is enhanced, a high power LED lamp can be made small in size and the luminous efficiency can be increased. If the projection angle are adjustable and the lights can be condensed, the problem of generating glare and dazzling would be avoided with enhanced luminous efficiency and increased luminous flux.